scostep 2010 (stp12) - Leibniz-Institut für Atmosphärenphysik an der ...

STP12 Abstracts
Berlin, 12 - 16 July 2010
SCOSTEP Symposium 2010
Why are relativistic electrons persistently quiet at geosynchronous orbit in 2009?
Kataoka Ryuho 1 , Miyoshi Yoshizumi 2
1 Tokyo Tech, 2 STEL, Nagoya University
Relativistic electrons at geosynchronous orbit (GEO) were persistently quiet in 2009 for
almost a whole year. The solar wind speed, which has been known as a primary parameter
controlling the outer belt electrons, was very slow in 2009 as expected, and at a comparably
low level as of 1997 when we did not observe such a persistently quiet condition. Since the
interplanetary magnetic field (IMF) was quite different between 1997 and 2009, the difference
in IMF is a possible cause of the difference in the electron flux levels, providing an important
clue to understand the complex source and loss process of relativistic electrons at GEO. We
suggest that the extremely weak IMF of the very slow solar wind plays an essential role in
diminishing the source processes themselves such as magnetic storms and substorms, and in
turn to suppress the relativistic electron flux at GEO over the time scale of a year, as an
inevitable consequence of extremely weak open magnetic field of the Sun associated with the
extremely weak current solar minimum.